In a conventional electronically controlled internal combustion engine using a single-point fuel injection system, a fuel injection valve is mounted on a throttle body defining an intake bore controlled by a throttle valve. The amount of fuel injection is controlled by a control unit according to the load condition of the engine as determined by the opening angle of the throttle valve, intake negative pressure, intake temperature and so on as well as the rotational speed of the engine. A typical single point fuel injection system is disclosed in Japanese patent laid open publication No. 58-122358.
In such a conventional single-point fuel injection system, there are so many accessory parts associated with the throttle body that the surrounding of the throttle body tends to be extremely crowded. This complicates the assembling process of the fuel injection system, and impairs the facility of servicing the fuel injection system. In particular, the wiring for the fuel injection valve and various sensors and the piping for the fuel injection valve are two major sources of problems.
Additionally, such a throttle body is typically equipped with a by-pass air passage controlled by a by-pass air control valve for controlling a flow of by-pass air by-passing the throttle valve and obtaining a favorable idling condition of the engine, and this also contributes to the complexity of the structure surrounding the throttle valve. A typical by-pass air control system is disclosed in Japanese patent laid open application No. 61-85543.